PDG-Arena: an ecophysiological model for characterizing tree-tree interactions in heterogeneous and mixed stands

Abstract

Key message: PDG-Arena, a new individual- and process-based ecophysiological model, was developed to simulate the functioning of mixed-species forests. It was evaluated using annual growth data on beech-fir stands of the French Prealps. Context: In the context of the ongoing climate and biodiversity crises, mixed forest stands are increasingly considered as a sustainable management alternative to monospecific and even-aged stands. Aims: We developed a new individual- and process-based forest growth model, PDG-Arena, to simulate mixed forest growth and functioning, and test ecophysiological interactions among trees in mixed stands. Methods: The model builds upon the validated ecophysiological stand-scale model CASTANEA and integrates tree competition for light and water. We evaluated the performance of PDG-Arena by comparing the simulated growth with annual radial growth data from 37 common beech and silver fir monospecific and mixed plots in the French Prealps. Results: PDG-Arena performed slightly better than CASTANEA when simulating even-age and monospecific forests (r2 of 32.1 versus 29.5%). When using structure-diverse and species-diverse inventories, PDG-Arena performed better than CASTANEA in pure beech (38.3 versus 22.9%) and mixed stands (40.5 versus 36.3%), but not in pure fir stands (39.8 versus 42.0%). The new model also showed a significant positive effect of species mixing on gross primary production (+ 5.5%), canopy absorbance (+ 11.1%), and transpiration (+ 15.8%) in the tested stands. Conclusions: Our results show that tree-level process-based models such as PDG-Arena, formally simulating interspecific interactions, can serve as a valuable tool to understand and simulate the carbon, radiative, and water dynamics of mixed stands.